Soak the lentils overnight. Drain and put in a saucepan with water to cover. Add the onion, bay leaf and salt to taste. Bring to the boil and simmer until the lentils are tender but not mushy, about 30 minutes. Drain and discard the onion and bay leaf. Chill.
Place the lentils in a serving bowl and sprinkle with the capsicum, spring onion and parsley. Combine the vinegar, olive oil and peanut oil and drizzle over the lentils. Grind over black pepper. This salad can marinate a few hours.